I prefer the big boats myself, but I started with SH4 as well. I saw it at Wal-Mart and thought "Holy crap! I haven't seen a subsim since I played Wolfpack and U-boat back in the day!"
After that, I got the expansion, and learned of SH3 and GWX.
If you are using stock SH3, I'd suggest GWX 2.1, as it does make things as real as a sim can get. The escorts and planes may have superhuman abilities sometimes, but that's what it was like for real Kaleuns.
Of course, any game, or mod, is still just a game, and games can be solved, but GWX does a damn good job of making it a difficult puzzle to solve. It's a big download, but every minute spent wating equates to hours of enjoyment (and tension, and frustration, which is what realism is about to a large degree
)
Good hunting!